The present invention relates to a method for making resilient hinges for spectacles.
As it is well known, resilient hinges for spectacles frames are presently commercially available which allow for the spectacles arms to be resiliently gradually biassed with respect to the spectacles frame front portion owing to the provision of resilient biassing means acting on a suitably shaped cam profile.
In particular resilient hinges are known of the so-called double action type, i.e. effective to provide a resilient reaction both in the arm opening step (that is with the spectacles arm parallel to one another during the use) and in the arm closure step, with the spectacles arm in a closed condition at rest.
The operating principle of the mentioned hinges is that of the resilient reaction provided by a cam profile on which a ball member is caused to slide as it is biassed by a spring.
In order to obtain an efficient and proper resilient reaction it is required that the cam member cooperating with said ball member, be made from a high hardness material.
In fact, if the hardness of said material is poor, the ball member would be susceptible to penetrate into the cam surface, thus impairing the cam effect thereof, because of wear.
Thus, the mentioned cam member is generally made starting from hardened steel or a sinterized material.
On the other hand, these materials are affected by practical drawbacks, since they are necessarily to be subjected to protecting treatments; moreover they may be hardly processed to obtain the desired shapes and coupling to other components of the frame.
More specifically, as thereinabove stated, the pieces made starting from the mentioned materials are to be suitably processed in order to prevent said pieces from being quickly oxidated.
The protecting covering layer, on the other hand, may be obtained only by carrying out determined processing steps (for example sealing of the steel cam member to the front of the spectacles frame) and, accordingly, other portions of the spectacles are affected, with consequent increased costs.
Moreover, a steel material may be hardly machined by tools, particularly as the conventional method for making not resilient hinges is used.
It should also be noted that presently available spectacles are provided with nickel silver hinges so shaped as to allow for the spectacles arm to be adjusted in its slant, in order to fit the spectacles to the user face.
On the other hand, the steel cam member is made in a single piece with the spectacles front portion, thereby it may be hardly subjected to modifications.
With respect to the applying and coupling features, it should be noted that, in plastics spectacles, the anchoring blade embedded in the spectacle front portion, acts as a cutting blade susceptible to cut through the spectacles as the latter are stressed during the use of because of temperature variations.
Moreover, because of contingent requirements, that is because of constructional reasons, the cam member is arranged at the outermost end of the spectacles frame, jointly to the front portion acting as an insert, thus facilitating possible breakages.